The present invention relates to reflective and transflective liquid crystal devices which use silver alloys and the like to reflect light, to a method for making the same, and to electronic apparatuses using the liquid crystal display devices as display sections.
As is well known, liquid crystal devices do not emit light but performs display by controlling the polarization state of light. Thus, it is necessary that the configuration be such that light is incident on a panel of the liquid crystal display device, and in this regard, they are quite different from other display devices, such as electroluminescent devices and plasma display devices.
Herein, the liquid crystal devices are classified into two types, that is, a transmissive type in which a light source is provided behind the panel and the light passing through the panel is observed by a viewer, and a reflective type in which the light incident from a viewer side and reflected by a panel is observed by a viewer.
In the transmissive type, the light emitted from the light source provided at the rear side of the panel is introduced to the entire panel through a light guide plate. Then, the light passes through a polarizer, a back substrate, an electrode, a liquid crystal, another electrode, a viewer-side substrate, and another polarizer and is observed by a viewer.
On the other hand, in the reflective type, the light incident on the panel passes through a polarizer, a viewer-side substrate, an electrode, a liquid crystal, and another electrode, is reflected by a reflective film, and passes through the path in the reverse direction, and is observed by a viewer.
As described above, the reflective type needs two paths including an incident path and a reflected path and large optical losses occur in both paths. Compared to the transmissive type, the amount of light from the surrounding environment (external light) is less than that of a light source disposed at the rear side of the panel. Since only a small amount of light is observed by the viewer, the display becomes dim. However, the reflective type also has noticeable advantages, such as high outdoor visibility under sunlight and an ability to display without a light source, compared with the transmissive type. Thus, the reflective liquid crystal display devices are widely used in display sections of portable electronic apparatuses and the like.
The reflective type, however, has a notable disadvantage in that the viewer cannot see the display when insufficient natural illumination is provided from the environment. In recent years, a transflective type has appeared in which a backlight is provided at the rear face of a panel, and a reflective film not only reflects the light incident from the viewer""s side but also transmits some of the light from the rear face. This transflective type functions both as a transmissive type by switching on the backlight to ensure visibility of the display when there is insufficient external light and as a reflective type by switching off the backlight in order to reduce power consumption when there is sufficient external light. This means, the transmissive type or the reflective type is selected depending on the intensity of the external light to ensure visibility of the display and to reduce power consumption.
In the reflective type and the transflective type, aluminum has been generally used as a material for the reflective film. However, in recent years, the use of elemental silver or a silver alloy primarily composed of silver (hereinafter referred to as merely xe2x80x9csilver alloyxe2x80x9d) has been investigated to improve reflectance for achieving bright display.
However, in a liquid crystal display device, a problem arises in that the reflectance of the reflective film formed of silver alloy or the like decreases when the film is subjected to a high-temperature treatment.
The present invention has been realized in view of the above circumstances. It is an object thereof to provide a liquid crystal device having a reflective film of a silver alloy or the like in which a decrease in reflectance does not occur during a high-temperature treatment, a method for making the device, and an electronic apparatus.
The present inventor concluded that a decrease in reflectance of the reflective film, which is composed of a silver alloy or the like, during the high-temperature treatment is caused by the crystal grain growth in the reflective film during the high-temperature treatment.
According to an aspect of the present invention, a liquid crystal device comprises a first substrate and a second substrate opposing each other and a liquid crystal enclosed in a gap between the first substrate and the second substrate, and the liquid crystal device further comprises a reflective film which is provided on the first substrate and contains silver, a protective film provided on the reflective film, a first transparent electrode provided on the protective film, and an alignment film provided on the first transparent electrode. According to such a configuration, the protective film is formed on the entire reflective film composed of silver alloy or the like. Since crystal grain growth in the reflective film is suppressed even if a high-temperature treatment of the alignment film is employed after the formation of the reflective film, a decrease in reflectance is prevented.
In this configuration, it is preferable that the liquid crystal device further comprises a first lead provided on the first substrate, wherein the first lead has a metal film, and the average diameter of the crystal grains in the metal film is larger than that of the crystal grains in the reflective film. Since a decrease in reflectance does not arise problems in the first lead, the resistance of this lead can be reduced by growing the crystal grains or by including large crystal grains.
It is preferable that the average diameter of the crystal grains in the reflective film be in the range of 0.1 nm to 6.0 nm, and the average diameter of the crystal grains in the metal film be in the range of 2.0 nm to 20 nm. By independently controlling the average diameters of the crystal grains in the reflective film and the metal film, both the reflective film and the lead exhibits optimized functions thereof.
Preferably, the metal film of the first lead is provided on the reflective film. That is, the metal film of the first lead is provided after the reflective film.
Preferably, the first lead further comprises a metal oxide film deposited on the metal film. The metal film is covered by the metal oxide film which is chemically more stable, and thus is prevented from corrosion.
In the configuration in which the liquid crystal device has the first lead, the liquid crystal device preferably further comprises a second transparent electrode provided on the second substrate, and a driver IC for supplying output signals to the first lead, the first lead being connected to the second transparent electrode with a conductor. Since the second transparent electrode provided on the second substrate is connected to the first lead provided on the first substrate by the conductor, all leads can be arranged on the first substrate side. The driver IC provided for supplying the output signals to the first lead contributes to a reduction in connections to the exterior.
Preferably, the metal film of the first lead is formed at a portion other than the connection to the driver IC so that the metal film is not provided at a portion to which stress is applied when the adhesiveness of the metal film to the substrate is insufficient.
In the configuration in which the liquid crystal device has the first lead, the liquid crystal device may further comprise a second lead provided on the first substrate, and a driver IC for driving the liquid crystal, wherein the second lead comprises a metal film, and an input signal is supplied to the driver IC through the second lead.
When the input signal is supplied to the driver IC through the second lead, the metal film is preferably formed at a portion other than the connection to the driver IC, since the adhesiveness of the metal film to the substrate is insufficient, as described above.
When the liquid crystal device is provided with the second lead, the liquid crystal device preferably further comprises an external circuit board for supplying the input signal to the driver IC, wherein the external circuit board is connected to the second lead, and the metal film is formed at a portion other than the connection to the external circuit board. Separation of the metal film is thereby prevented when the external circuit board is repaired.
The liquid crystal device may further comprises a first lead connected to the first transparent electrode, and a driver IC connected to the first lead, wherein the first lead comprises a metal film. In this configuration, the driver IC supplies signals to the first transparent electrode through the first lead.
Preferably, the metal film of the first lead is formed at a portion other than the connection to the driver IC, since the adhesiveness of the metal film to the substrate may be insufficient.
Alternatively, when the first lead is connected to the first transparent electrode, the liquid crystal device may further comprises a second lead provided on the first substrate, wherein the second lead comprises a metal film, and an input signal is supplied to the driver IC through the second lead.
When the second lead is provided, the liquid crystal device may further comprises an external circuit board supplying an input signal to the second lead, wherein the metal film of the second lead is formed at a portion other than the connection to the external circuit board.
Since an electronic apparatus according to an aspect of the present invention comprises the above liquid crystal device, a decreased in reflectance of the reflective film is suppressed, enabling bright display.
When the reflective film contains silver, the reflectance-vs.-wavelength characteristics thereof are not as flat as those of aluminum which is generally used, and the reflectance decreases at the lower wavelength end. As a result, the light reflected by the reflective conductive film containing silver less contains the blue light component and thus is yellowish. According to an aspect of the present invention, a liquid crystal device comprises a first substrate and a second substrate opposing each other and a liquid crystal enclosed in a gap between the first substrate and the second substrate; and the liquid crystal device further comprises a reflective film which is provided on the first substrate and contains silver, and a protective film provided on the reflective film, wherein the reflectance of the protective film for (blue) light at the shorter wavelength end of visible light is higher than that for (green and red) light at the longer wavelength end. In such a configuration, large amounts of blue light components are reflected by the protective film before being reflected by the reflective film; hence, the light obtained by recombining the light reflected by the protective film and the light reflected by the reflective film containing silver is not yellowish.
The protective film may contain titanium oxide and preferably has a refractive index of 1.8 or more.
In order to obtain reflected light which is not yellowish, a correction using color layer is also useful, instead of the above configuration such that large amounts of blue light components are reflected by the protective film. According to an aspect of the present invention, a liquid crystal device comprises a first substrate and a second substrate opposing each other and a liquid crystal enclosed in a gap between the first substrate and the second substrate; and the liquid crystal device further comprises a reflective film which is provided on the first substrate and contains silver; first transparent electrodes provided on the reflective film, and second transparent electrodes provided on the second substrate, wherein dots are formed corresponding to crossings of the first transparent electrodes and the second transparent electrodes, a plurality of the dots defining one pixel, different color layers are assigned to the dots defining said one pixel, the color layers containing a blue color layer and a red color layer, and the distance from the white coordinate point to the coordinate point of the light which passes through the blue color layer is larger than the distance from the white coordinate point to the coordinate point of the light which passes through the red color layer in an xy chromaticity diagram (CIE1931). Since the conductive layer enhances the blue light compared to the red light in this configuration, the reflected light is not yellowish.
According to an aspect of the present invention, a liquid crystal device comprises a first substrate and a second substrate opposing each other and a liquid crystal enclosed in a gap between the first substrate and the second substrate; and the liquid crystal device further comprises a reflective film which is provided on the first substrate and contains metal; a first transparent electrode deposited on the reflective film; and a lead provided on the first substrate, wherein the lead comprises a metal film, and the average diameter of the crystal grains in the metal film is larger than that of the crystal grains in the reflective film.
In such a configuration, the liquid crystal device preferably further comprises a first extending region which is provided at one side of the first substrate and which does not overlap the second substrate, and a second extending region which is provided at a side crossing said one side of the first substrate and which does not overlap the second substrate, wherein the lead is provided over the first extending region and the second extending region.
According to an aspect of the present invention, a method for making a liquid crystal device comprising a first substrate and a second substrate opposing each other and a liquid crystal enclosed in a gap between the first substrate and the second substrate, the method comprises the steps of: providing a reflective film containing silver on the first substrate; providing a protective film on the reflective film; providing a first transparent electrode on the protective film; and providing an alignment film on the first transparent electrode. Since crystal grain growth is suppressed in the reflective film during a high-temperature treatment of the alignment film after the reflective film is formed, the reflectance does not decrease.
Preferably, the method further comprises the step of providing a first lead having a metal film on the first substrate, wherein the average diameter of the crystal grains in the metal film is larger than that of the crystal grains in the reflective film.
According to an aspect of the present invention, a method for making a liquid crystal device comprising a first substrate and a second substrate opposing each other and a liquid crystal enclosed in a gap between the first substrate and the second substrate, the method comprises the steps of providing a reflective film containing silver on the first substrate, and providing a protective film on the reflective film, wherein the reflectance for light at a shorter wavelength end in visible light of the protective film is higher than that for light at a longer wavelength end. Since large amounts of blue light components are reflected by the protective film before the component is reflected by the reflective layer, the light obtained by recombining the light reflected by the protective film and the light reflected by the reflective film containing silver is not yellowish.
The protective film may contain titanium oxide and may have a refractive index of 1.8 or more.